Vehicles having internal combustion engines employ fuel delivery systems with fuel tanks. Emission control systems may be provided in these vehicles to absorb fuel vapors generated during refueling events, during diurnal cycles, and during vehicle run time. An emission control system may include a fuel vapor canister coupled to the fuel tank configured to store fuel vapor in an adsorbent bed. The adsorbed fuel vapor may then be purged to an engine intake for combustion.
In vehicles such as hybrid-electric vehicles (HEVs) and other vehicles configured to operate for periods without combusting fuel, opportunities to purge the fuel vapor canister may be limited. In order to prevent run time losses from saturating the fuel vapor canister, a fuel tank isolation valve (FTIV) may be coupled between the fuel tank and the fuel vapor canister. By keeping the FTIV closed, fuel vapor remains trapped within the fuel tank. The FTIV may be opened to vent the fuel tank, and to allow refueling vapors to be flowed to the fuel vapor canister. As such, the FTIV may be closed during most periods of engine operation. However, FTIV's, among other solenoid valves, use a considerable amount of battery power to remain energized. Therefore, hatchable valves may be used to reduce the power consumption as well as the cost of the valve.
US 2012/0211087 discloses an electrically latchable FTIV. The latchable FTIV is pulsed via current to actuate the valve between a closed and open position. A controller (e.g., powertrain control module) keeps track of the valve position in memory. However, the valve position information may become invalid or indeterminate for a number of reasons such as tow battery, reflashing of the controller, memory corruption in the controller, and valve replacement. Invalid valve position information leaves the emission control system in an undesirable state which may lead to increased emissions. In order to determine the position of the valve, the valve may be actuated and a state of the fuel tank and/or emissions control system evaluated for change. This may take a considerable amount of time, and/or place the valve in a non-optimal position. In other examples, a dedicated position sensor may be coupled to the valve, though this may increase the cost and complexity of the valve, may require additional solenoid wiring, and may further require additional OBD testing to monitor the function of the position sensor.
The inventors herein have recognized the above issues, and have developed systems and methods to at least partially address them. In one example, a fuel system is provided, the fuel system comprising a fuel tank isolation valve coupled between a fuel tank and a fuel vapor canister. The fuel tank isolation valve comprises an actuation coil comprising a first terminal wire and a second terminal wire, the actuation coil configured to generate a magnetic field when the first and second terminal wires are switchably connected to an actuating voltage source, and a valve shaft at least partially disposed within the actuation coil, the valve shaft configured to change between an open position and a closed position in response to the actuation coil generating a magnetic field having a flux density above a threshold, wherein the valve shaft is configured to alternately latch in the open and closed positions such that the valve shaft is maintained in a latched-open or latched-closed position when the actuation coil is generating a magnetic field having a flux density below the threshold, and wherein the fuel tank and the fuel vapor canister are fluidically coupled when the valve shaft is in the open position but not when the valve shaft is in the closed position. The fuel system further comprises a controller configured to indicate a position of the valve shaft based on a measured current-voltage relationship between the first and second terminal wires during a condition in which the magnetic field generated by current through the actuation coil has a flux density below the threshold. In this way, the position of the valve shaft may be determined without adjusting the position of the valve shaft. In one example, the valve shaft includes an indicator coil that is selectively electrically coupled to the actuation coil based on valve shaft position. In this way, the measured current-voltage relationship between the first and second terminal wires may be significantly and predictably different when the valve shaft alternates between the open and closed positions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter s not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.